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It seems like every week, I can do an article on some interesting science that ended up buried under hyperbolic headlines and overly credible coverage. This week's victim is "living concrete." It only sort of exists, in that the material can either be living or concrete, but not really both. It doesn't heal itself either. But none of that means the publication has no merit, as it does show that the concept more or less works, and it identifies a number of areas that need further study in order for "living concrete" to actually become useful.

La vida concrete

The idea of mixing living things and concrete isn't quite as strange as it sounds. Part of concrete's strength comes from carbonates that are formed during the curing process. Lots of living things also produce structures made of carbonates; these include some very robust structures that are a mix of proteins and carbonates, like the shells of many aquatic animals.

As such, there's been a lot of research around the periphery of structural concrete that has involved biology. This has mostly involved lots of work on trying to figure out how the shells of living creatures get some of their impressive properties. But it has also included the idea that living things could form structural carbonates, including a few attempts to make concrete that self-heals thanks to the presence of carbonate-producing microbes embedded in it.

The problem here is that the environment of concrete is not especially compatible with anything staying alive. The initial setting of concrete releases a lot of heat, and the pH remains very high long after the concrete sets. So, all of these attempts have involved finding some way of protecting the "living" portion of things from the "concrete" part.

The new work, done by a team at the University of Colorado in Boulder, avoids the concrete issue entirely. Instead, it tries to make carbonates produced by living things one of the main structural components of their material. It works, but not especially brilliantly.

It's alive!

The first step the authors focused on was finding the right organism to produce the carbonates. Ideally, they want something that doesn't need a lot of care—something they can just set up in their material and ignore for a while. They settled on a species of photosynthetic bacteria called Synechococcus, a type of cyanobacteria. This has the advantage of not needing any special carbon source to produce carbonate, since it gets what it needs by pulling carbon dioxide out of the air. Cyanobacteria also tend to live in aquatic environments, and so many species are adept at pulling what they need to survive out of a sparse environment.

Concrete is typically a mix of a binding material and structural fill. The living concrete was no different. For the fill, the researchers used a cheap material: sand.

This left a major challenge. Forming carbonates is a slow process, so the cyanobacteria wouldn't be playing any structural role for a while after they are placed in with the sand. So how do you keep the material together long enough for the carbonates to form? The answer they settled on was simple and definitely biologically compatible: gelatin, the material used to make soft, jelly-like foods.

The researchers mixed the gelatin and bacteria and suspended sand in the mixture. This was enough to maintain simple structures for long enough that the cyanobacteria could start forming carbonates.

As long as the mixture was kept at an ambient humidity of 50 percent or more, the gelatin would absorb enough water to maintain a hydrogel that supported bacterial life for at least a week. The metabolic activity of the cyanobacteria could also be adjusted via the temperature: kept at just above freezing, and the bacteria would live longer but wouldn't deposit much carbonate; heat things up to above room temperature, and there would be more carbonate, but the survival went down.

As long as enough was done to keep some of the bugs alive, the authors showed that you could pull some of the cyanobacteria out of one structure and use them to inoculate a new one. And you could continue that process through at least three generations of structures. (Possibly more, but you've got to stop and write the paper at some point.)

So, why isn't this exciting?

The big problem here is that, as long as the gelatin is kept hydrated, the material is literally held together with jello. The cyanobacteria simply don't produce enough carbonate within a week to give the "concrete" the sort of material toughness we associate with actual concrete. To do better, you actually have to dry the whole thing out, killing the bacteria in the process. As the gelatin dries out, it forms a mesh of protein mixed with the calcium carbonate formed by the cyanobacteria (which is a mix of calcite and gypsum). This binds the sand together, forming a robust structure.

This is why the material can be living or a concrete, but not both at the same time. This is also why it's not really a self-healing material. It could self-heal, but only if kept in a floppy, gelatinous state.

A dried gelatin mesh around sand would be a fairly robust material. But the presence of the cyanobacteria improved its resistance to fracture by over 15 percent. It also held up to compression about as well as a low-grade cement, although that was largely down to the sand within the mixture. In any case, the presence of cyanobacteria made the material more robust than gelatin alone. None of these numbers is especially impressive, but it's entirely possible that the amount of carbonate would continue to go up over time, and the strength of the dried material would go up with it.

In fact, most of this work trails off into a set of possibilities. It might be possible to select the cyanobacteria so that it evolves a greater tolerance to drier conditions, and thus they live longer within the solidifying material. What we could potentially enhance is carbonate production, so that more of the material is produced while the cyanobacteria are alive. We could replace the gelatin with a material that forms a robust mesh while water levels are still high. Of course, all of this is predicated on a large unknown: we don't know if more carbonate will actually improve the material's robustness.

All of this makes the paper an intriguing early effort worth some attention. But the researchers really need to think more about how they're presenting a preliminary study like this. The phrase "living concrete" doesn't exist anywhere in the paper—in fact, the authors state that the new materials "are not intended to broadly replace cementitious materials." But the phrase is in the title of the press release that launched all those headlines. The researchers do refer to making "living building materials" in the paper, but it's not clear what, exactly, could be built using the materials in their present state of development.

73 Reader Comments

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

Well you still need heat to dry it out and make it a viable concrete, we also dont know how long the process takes or how well it scales

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

I believe I read an article recently on the concrete used by ancient Romans being "self healing", as well as having the benefits you describe. These were structures in salt water - jetties, quays, etc - that still exist.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

I believe I read an article recently on the concrete used by ancient Romans being "self healing", as well as having the benefits you describe. These were structures in salt water - jetties, quays, etc - that still exist.

Roman Concrete generally used volcanic ash, there isnt that much laying around, and the closest substitute we have that will work more or less the same is coal ash.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

I believe I read an article recently on the concrete used by ancient Romans being "self healing", as well as having the benefits you describe. These were structures in salt water - jetties, quays, etc - that still exist.

I'm not sure about that either way, but I do know there's common misconceptions around Roman concrete. People like to glorify it and say they had some secret special sauce modern science doesn't understand, and that's why Roman buildings are still standing.

Rather, it's just due to Roman concrete not using rebar. It's the rebar rusting and shifting that leads to failures in modern structures. Roman structures were designed entirely with compression, like arches and pillars. If they had iron/steel rebar and used it to build overhanging structures like we do, they'd be in shambles by now.

As I understand it they did have a formula that was good at the time due to (perhaps among other things) the incorporation of volcanic ash. However, modern concrete is superior in every way.

This reminds me of the story I just read about how supposedly future colonists to the moon and Mars will be living in structures grown from fungus. Sure they will.

Seems a little bit out there to me, but that reminds me of something that seems a tad more realistic: making food-packaging, disposable plates, cups and utensils and similar things out of some form of fungus. It'd all be edible -- though not perhaps particularly tasty -- and completely biodegradable all naturally. Can't remember where I read about the plans for that anymore, but someone was actually researching it.

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

I believe I read an article recently on the concrete used by ancient Romans being "self healing", as well as having the benefits you describe. These were structures in salt water - jetties, quays, etc - that still exist.

Actually I do not understand why there is no more followup researches on it. Seems like a cheap and nature-conscious (albeit slow) way to build undersea structures (or even boats. yes, concrete boat hull is a thing).

There are mentions (maybe not in the paper but in the biorock site) that the chemistry of the resulting biorock is similar to the concrete used by Romans, and they refer those still existing jetties. However when I did some reading into that angle, it seemed for me that roman concrete have different chemistry. That could be a misunderstanding from my part though.

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

I don't think that we would run out of sand globally soon, given the size of deserts worldwide. Running out of cheaply and legally extractable sand locally is another issue. Paying the costs which were externalized before is of course a problem for any industry, but it is needed for sustainability.And the fact that the particles of desert sand are too smooth for some uses is yet another one.

But sand is just one of the possible filler materials for concrete, so I don't think that even its shortage would stop humanity from building concrete structures.

Actually I do not understand why there is no more followup researches on it. Seems like a cheap and nature-conscious (albeit slow) way to build undersea structures (or even boats. yes, concrete boat hull is a thing).

It isn't at all cheap. It's reversing redox reactions, which takes a tremendous energy input on a joule-per-mol basis. And what you get out of it is limestone and milk of magnesia, which is tough stuff to a coral but pretty weak by human standards.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

Well you still need heat to dry it out and make it a viable concrete, we also dont know how long the process takes or how well it scales

Concrete accounts for about 5% of our CO2 released every year (about half that of air travel).

The idea of using carbon-capturing, instead of carbon-releasing, concrete is an attractive one, but there are a lot of caveats to that.

Since these are organic in origin, they're inherently going to contain voids from the critters that were in them and died. Whether there's CO2 out-gassing from their decay isn't really as concerning as what happens to concrete with voids in it, even microscopic ones. Structurally, it is much less strong than if there are no voids.

The mixing of concrete is a bit of a science in and of itself, but the use of low-grade concrete is viable in almost every construction project, as long as one uses enough of it. The trouble is, beams, columns and other such slender load-bearing concrete structures would be considerably thicker as a result, and that increases both construction time and costs.

Using a low-grade concrete with billions of microscopic voids from the dead critters that contributed the carbonates to create the rigid structure would detrimentally impact the strength of the low-grade concrete one can make from it. Depending on the use and design, it may not be a viable option for construction - especially load-bearing structural construction. Decorative construction and non-load-bearing uses are viable, though.

So, I don't foresee this being used to REPLACE concrete because it won't have the necessary strength in any of the cases where we use design mix concrete. But nominal mix may be better suited to it, depending on the necessary strength, and wear resistance it has.

A lot more work needs to be done to prove the viability of the concept, but the research certainly looks interesting. If they can reduce the "don't touch this yet" cure time to something reasonable and improve the strength, while reducing or matching current costs, it's worth a look. If it's significantly more expensive than concrete is today, then that will have to be addressed before it will be used outside of niche projects.

Not sure I care for that shade of green, though. (Even though it goes away to another color - a yellow orange, IIRC - after the critters dry out and die.)

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

I don't think that we would run out of sand globally soon, given the size of deserts worldwide. Running out of cheaply and legally extractable sand locally is another issue. Paying the costs which were externalized before is of course a problem for any industry, but it is needed for sustainability.And the fact that the particles of desert sand are too smooth for some uses is yet another one.

But sand is just one of the possible filler materials for concrete, so I don't think that even its shortage would stop humanity from building concrete structures.

Sand is the lesser of the fillers. It binds with the cement to the aggregate, filling in voids. The aggregate is what provides structural strength. The more sand there is, the less the strength of the concrete.

As for the issue with desert sand, that's a matter of what kind of binding materials are used. Cement is typically a limestone powder providing the carbonate plus other elements like aluminum, silicone, iron which alter the binding power of the cement. They're working on a binding agent that can work with desert sand, so it's not like it can't be used. It just can't be used with current methods of creating concrete.

The BBC had a good article on why we are running out of sand - at least the good type that is (currently) used in concrete and also how the removal of sand is destroying the Meekong Delta.

It's a problem - honestly my hope is that some of the really interesting materials research into alternative building materials (e.g. Finite) will get to a point where we actually can deliver something with less of an energy/carbon footprint and use a wider variety of aggregates/fillers.

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

I don't think that we would run out of sand globally soon, given the size of deserts worldwide. Running out of cheaply and legally extractable sand locally is another issue. Paying the costs which were externalized before is of course a problem for any industry, but it is needed for sustainability.And the fact that the particles of desert sand are too smooth for some uses is yet another one.

But sand is just one of the possible filler materials for concrete, so I don't think that even its shortage would stop humanity from building concrete structures.

Like with oil, yes there's still plenty around, but worldwide construction is already facing a significant sand shortage. Desert sand is largely useless and places like Dubhai and Mauritania which are within sand deserts import all thier concrete sand which now that vietnam and indonesia have banned exporting sand both face serious shortages.Construction in china has been seriously impacted as well with illegal dregging actually blamed for bridge collapses not to mention China's various ghost cities where so little sand was used in mix (cost savings) that you can often lightly kick thru some concrete structures.Even in north america sand used in concrete has been steadily rising in price and estimates of remaining sources are beginning to worry analysts. Its a commodity like fresh water that tye demand is begining to threaten suply

An alternative to sand would be very useful ... We haven't really got one yet, And that was kinda my point.

[The cyanobacteria] gets what it needs by pulling carbon dioxide out of the air.

So, can a process like this be tinkered into a CO2 capture/sequestration system?

That same line made me wonder it this might be a good choice for the creation of artificial coral reefs. I've seen articles in the past where people make artificial coral reefs out of concrete, and I can't help but wonder if this stuff might make a good alternative.

Desert sand makes weak concrete, all the jagged edges are rounded by erosion.

About a decade ago my wife and I finally moved to the farm of our dreams, and I set about planning a horse arena for her. The key issue in a riding arena is the 'footing'...the qualities of the surface material.

An engineer friend swept me off on a field trip, visiting every riding arena we could find for miles around. This is a pretty horsey area, so that was a lot of arenas. Some were like sand dunes, far too soft to walk easily on; a cantering horse would constantly be dragging his feet, risking a stumble; not cool. Others were hard as a rock...not something I'd want to fall onto, and also far too tough on a horse's legs. Only a few were just right. We took measurements of the average sand depth (usually laid atop a base of compacted stone screenings). Using a field microscope, we noted the sand's relevant micro-characteristics, from size distribution and grain morphology (jagged versus rounded) to color, translucence, packing behavior, and non-sand contaminants. We collected samples, took them home, dried them in an oven, and weighed packed samples of fixed volume.

I learned a ton about sand in the process, and managed to achieve a footing for our arena that more than a few expert dressage riders have pronounced "perfect." The most fun part of the effort was making a pain in the ass of myself at numerous sand quarries and distributors' yards. You could practically hear them thinking "WTF?" as I pulled out my field microscope to inspect their wares.

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

I don't think that we would run out of sand globally soon, given the size of deserts worldwide. Running out of cheaply and legally extractable sand locally is another issue. Paying the costs which were externalized before is of course a problem for any industry, but it is needed for sustainability.And the fact that the particles of desert sand are too smooth for some uses is yet another one.

But sand is just one of the possible filler materials for concrete, so I don't think that even its shortage would stop humanity from building concrete structures.

Like with oil, yes there's still plenty around, but worldwide construction is already facing a significant sand shortage. Desert sand is largely useless and places like Dubhai and Mauritania which are within sand deserts import all thier concrete sand which now that vietnam and indonesia have banned exporting sand both face serious shortages.Construction in china has been seriously impacted as well with illegal dregging actually blamed for bridge collapses not to mention China's various ghost cities where so little sand was used in mix (cost savings) that you can often lightly kick thru some concrete structures.Even in north america sand used in concrete has been steadily rising in price and estimates of remaining sources are beginning to worry analysts. Its a commodity like fresh water that tye demand is begining to threaten suply

An alternative to sand would be very useful ... We haven't really got one yet, And that was kinda my point.

desert sand can't be readily used in concrete (for same properties as river sand) as the grains are to smooth

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

I don't think that we would run out of sand globally soon, given the size of deserts worldwide. Running out of cheaply and legally extractable sand locally is another issue. Paying the costs which were externalized before is of course a problem for any industry, but it is needed for sustainability.And the fact that the particles of desert sand are too smooth for some uses is yet another one.

But sand is just one of the possible filler materials for concrete, so I don't think that even its shortage would stop humanity from building concrete structures.

Like with oil, yes there's still plenty around, but worldwide construction is already facing a significant sand shortage. Desert sand is largely useless and places like Dubhai and Mauritania which are within sand deserts import all thier concrete sand which now that vietnam and indonesia have banned exporting sand both face serious shortages.Construction in china has been seriously impacted as well with illegal dregging actually blamed for bridge collapses not to mention China's various ghost cities where so little sand was used in mix (cost savings) that you can often lightly kick thru some concrete structures.Even in north america sand used in concrete has been steadily rising in price and estimates of remaining sources are beginning to worry analysts. Its a commodity like fresh water that tye demand is begining to threaten suply

An alternative to sand would be very useful ... We haven't really got one yet, And that was kinda my point.

desert sand can't be readily used in concrete (for same properties as river sand) as the grains are to smooth

Interesting research but Isn't one if the primary rising issues with modern concrete besides its energy /carbon load in manufacturing the fact that we are simply running out of sand? At least of the type suitable for concrete with illegal dredging of rivers becoming a thing world wide? I know its not the point of research but does seem like a bit of a hitch.

I don't think that we would run out of sand globally soon, given the size of deserts worldwide. Running out of cheaply and legally extractable sand locally is another issue. Paying the costs which were externalized before is of course a problem for any industry, but it is needed for sustainability.And the fact that the particles of desert sand are too smooth for some uses is yet another one.

But sand is just one of the possible filler materials for concrete, so I don't think that even its shortage would stop humanity from building concrete structures.

The vast majority of sand in the planet is not suitable for concrete. Sand used in concrete mixes must have sand grains that are rough and freshly fractured. Sand that has been polished by wind or water is unsuitable. In fact, even Saudi Arabia imports sand for their construction projects even though the county is pretty m much all sand.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

I believe I read an article recently on the concrete used by ancient Romans being "self healing", as well as having the benefits you describe. These were structures in salt water - jetties, quays, etc - that still exist.

I'm not sure about that either way, but I do know there's common misconceptions around Roman concrete. People like to glorify it and say they had some secret special sauce modern science doesn't understand, and that's why Roman buildings are still standing.

Rather, it's just due to Roman concrete not using rebar. It's the rebar rusting and shifting that leads to failures in modern structures. Roman structures were designed entirely with compression, like arches and pillars. If they had iron/steel rebar and used it to build overhanging structures like we do, they'd be in shambles by now.

As I understand it they did have a formula that was good at the time due to (perhaps among other things) the incorporation of volcanic ash. However, modern concrete is superior in every way.

I disagree with that final sentence. The pozzolanic cement used by the Romans is much more durable in a saltwater environment than modern Portland cement is. The rebar point is entirely valid.

Surely the potential benefit is the elimination of the high temperature, carbon dioxide releasing processes involved in concrete making?If diatoms and snails can produce strong structures at room temperature, and that can be replicated, the embedded energy of many building materials could be drastically reduced.

I believe I read an article recently on the concrete used by ancient Romans being "self healing", as well as having the benefits you describe. These were structures in salt water - jetties, quays, etc - that still exist.

I'm not sure about that either way, but I do know there's common misconceptions around Roman concrete. People like to glorify it and say they had some secret special sauce modern science doesn't understand, and that's why Roman buildings are still standing.

Rather, it's just due to Roman concrete not using rebar. It's the rebar rusting and shifting that leads to failures in modern structures. Roman structures were designed entirely with compression, like arches and pillars. If they had iron/steel rebar and used it to build overhanging structures like we do, they'd be in shambles by now.

As I understand it they did have a formula that was good at the time due to (perhaps among other things) the incorporation of volcanic ash. However, modern concrete is superior in every way.

I disagree with that final sentence. The pozzolanic cement used by the Romans is much more durable in a saltwater environment than modern Portland cement is. The rebar point is entirely valid.

[The cyanobacteria] gets what it needs by pulling carbon dioxide out of the air.

So, can a process like this be tinkered into a CO2 capture/sequestration system?

For this material to be carbon-neutral or better we would first need to have a source of gelatin (or a good substitute) that isn't made from animals.

For food products, gelatin can often be substituted with agar - which is made from algae. The problem with agar is that it needs to be dissolved at a higher temperature than gelatin, which would increase the risk of killing the cyanobacteria in the solution.Some Chinese scientists have found a way to produce gelatin using GMO yeast though.